Method for generating a signal responsive to the induction air temperature of an internal combustion engine

ABSTRACT

A method for generating a signal (TAn) responsive to the induction air temperature of an internal combustion engine. The signal (TAn) for the induction air temperature is determined from a signal (TMot) for the temperature of the internal combustion engine, from a signal (TU) for the ambient temperature, and from a correction factor K. Correction factor K is a function of a signal (mL) and/or a vehicular speed signal (v), signal (mL) representing either the induction air quantity or the air mass of the internal combustion engine. To enable the most accurate possible simulation of induction air temperature, even under changing operating conditions, the signal (TAn) for the induction air temperature is filtered, it being possible to variably select the time constant (ZK) of the filter in response to rising and falling induction air temperatures.

FIELD OF THE INVENTION

The present invention relates to a method for generating a signalresponsive to the induction air temperature of an internal combustionengine.

BACKGROUND INFORMATION

In present-day internal combustion engines, the metered fuel flow isprecisely adjusted to the induction air quantity of the internalcombustion engine. The air quantity is determined by an appropriatemeasuring process. In this process, for example, a pressure sensormounted in the intake tract of the internal combustion takes a pressuremeasurement and, to determine the air quantity, the thus obtainedpressure information is corrected as a function of the induction airtemperature to compensate for the temperature dependency of the airdensity. The induction air temperature is ascertained by a temperaturesensor mounted in the intake tract of the internal combustion engine.However, the accuracy of the temperature sensing may be adverselyaffected when heat produced by high temperatures in the enginecompartment radiates to the temperature sensor and its surroundings.

Moreover, the temperature sensor has a certain inertia, so that theaccuracy of the temperature sensing may likewise be adversely affected,especially when subjected to rapid temperature changes in the inductionair, for example when the vehicle is accelerating. The object of thepresent invention is to make available a signal which will reproduce theinduction air temperature very accurately. Advantageous embodiments ofthe method according to this following.

SUMMARY OF THE INVENTION

The principal advantage of the present invention is that it enables theinduction air temperature of the internal combustion engine to bedetermined very precisely. In the process of the present invention, asignal is generated for the induction air temperature on the basis of asignal for the temperature of the internal combustion engine and asignal for the ambient temperature. The advantage of this process isthat the need has been eliminated for a sensor to detect induction airtemperature. Engine-temperature and ambient-temperature sensors are, asa rule, already present anyway.

When the signal is generated for the induction air temperature, acorrection factor, which is a function of a signal for the induction airmass or air quantity of the internal combustion engine and of a signalfor vehicular speed, is taken into consideration.

It is especially advantageous for the signal for the induction airtemperature to be filtered, since this enables the dynamic behavior timeresponse to be simulated very precisely. Different time constants areexpediently used for the filtering process when working with rising andfalling induction air temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a basic representation of the technical area where thepresent invention can be used.

FIG. 2 depicts a flow chart for illustrating the method of the presentinvention; and

FIG. 3 depicts a table of a characteristics map employed in the methodof the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of the technical area where theinvention can be used. An air/fuel mixture is supplied via an intaketract 102 to an internal combustion engine 100, and the exhaust gasesare given off into an exhaust duct 104. Arranged in intake tract102--viewed in the flow direction of the induction air--are an air-flowsensor or mass air-flow sensor 106--for example a hot-film air-massmeter, a throttle valve 108 with a sensor 110 for detecting the openingangle of throttle valve 108, a pressure sensor 112, and at least: oneinjection nozzle 114. As a rule, either mass air-flow sensor 106 orpressure sensor 112 are alternatively provided. Mounted on internalcombustion engine 100 are an engine speed sensor 116 and a temperaturesensor 118. In addition, internal combustion engine 100 has, forexample, four spark plugs 120 for igniting the air/fuel mixture in thecylinders. A temperature sensor 121 for determining the ambienttemperature is mounted at an appropriate location on the motor vehicle,for example in the exterior mirror. The output signals mL from theair-flow sensor or mass air-flow sensor 106, α of sensor 110 fordetermining the opening angle of throttle valve 108, P of pressuresensor 112 (as a rule, alternatively to signal mL), n of engine speedsensor 116, TMot of temperature sensor 118, and TU of temperature sensor121 are fed via appropriate connector leads to a central control unit122. By way of other connector leads, control unit 122 controlsinjector(s) 114 and spark plugs 120. In addition, the control unitcarries out the method of the invention.

FIG. 2 shows a flow chart for illustrating the method of the invention.In a first step 200, internal combustion engine 100 is started. Step 200is followed by a step 202, in which the temperature of internalcombustion engine look is detected and is held ready as a signal TMot.Step 202 is followed by a step 204, in which a signal TAnF, whichrepresents a filtered value of the induction air temperature, is set toa value indicating the signal TMot for the temperature of internalcombustion engine 100. Step 204 is used for initialization purposes and,as a rule, is performed only once immediately after internal combustionengine 100 is started. After that, signal TAnF is determined inaccordance with the method described in the following.

Step 204 is followed by a step 206, in which a number of operatingparameters are determined which are required for generating the filteredsignal TAnF for the temperature of the induction air of internalcombustion engine 100. In particular, of signal mL for the induction airquantity or air mass of internal combustion engine 100, signal v forvehicular speed, signal TMot for the temperature of internal combustionengine 100, and signal TU for the ambient temperature are detected.Signal mL can be generated by the air-flow sensor or mass air-flowsensor 106 or be determined from the signal P of pressure sensor 112 andfrom signal n of engine speed sensor 116. Step 206 is followed by a step208. In step 208, a correction factor K is read out of a characteristicsmap which is set up to include the induction air mass or air quantity mLand the vehicular speed v. Instead of this characteristics map, acharacteristic curve can also be used, which is stored as a function ofthe air quantity or air mass mL (i.e., correction factor K can also besolely a function of air quantity or air mass mL). Step 208 is followedby a step 210, in which a signal TAn for the temperature of theinduction air of internal combustion engine 100 is determined fromsignals TMot and TU determined in step 206 and from correction factor Kdetermined in step 208. The correction factor K is multiplied by thedifference of signals TMot and TU representing the engine temperatureand the ambient temperature respectively. This multiplication product issubtracted from signal TMot for the engine temperature and, in thismanner, a value is determined for lagging of signal TAn.

To allow for the induction air temperature, with a certain inertia,behind a rapid change in the operating conditions, and since intaketract 102 acts as a heat accumulator, signal TAn for the induction airtemperature is filtered. The filtering can take place for rising andfalling induction air temperature with different time constants ZK1 andZK2. In particular, the following steps are carried out in connectionwith the filtering process:

Query 212 following step 210 questions whether the value TAn(I) of theinduction air temperature is greater than the preceding value TAn (I-1).If this is the case, then the temperature of the induction air rises andquery 212 is followed by a step 214, where value ZKl is assigned to timeconstant ZK. If, on the other hand, query 212 is not satisfied, i.e.,the temperature of the induction air drops, then query 212 is followedby a step 216, where a value ZK2 is assigned to the time constant ZK.Both step 214 as well as step 216 are followed by a step 218. In step218, a filtered signal TAnF is determined for the temperature of theinduction air. For that, the temperature of two sequential values TAn(I) and TAn (I-1) of the induction air temperature are multiplied bytime constant ZK. This multiplication product is added to the value TAn(I-1) for the induction air temperature. The filtered signal TAnF forthe induction air temperature can then be fed to the desiredapplications. It can be used, for example, to correct the signal P forthe pressure prevailing in the intake tract or signal mL for theinduction air quantity or air mass. The cycle through the flow chartends with step 218 and begins again with step 206.

FIG. 3 shows one possible calculation for the characteristics map fordetermining correction factor K, which is set up to include the signalsv for the vehicular speed and mL for the induction air quantity or airmass of internal combustion engine 100. At a very low vehicular speed(e.g., when the vehicle is at a standstill), and at a very low inductionair quantity or air mass (e.g., when the vehicle is idling), thecorrection factor K has the value 0. Thus, the calculation performed instep 210 of FIG. 2 leads to signal TAn for the temperature of theinduction air being equal to the signal TMot for the temperature ofinternal combustion engine 100. In another extreme case, at a very highvehicular speed and a very high induction air quantity or air mass, thecorrection factor K has the value 1. Therefore, the calculation inaccordance with step 210 of FIG. 2 leads to the signal TAn for theinduction air temperature being equal to the signal TU for the ambienttemperature. Thus, the induction air temperature varies between thetemperature of internal combustion engine 100 and the ambienttemperature depending on how quickly the vehicle is moving and which airquantity or air mass is drawn in by the internal combustion engine.

What is claimed is:
 1. A method for generating an induction airtemperature signal, comprising the steps of:providing a temperaturesignal indicative of a temperature of an internal combustion engine;providing an ambient air temperature signal; and generating theinduction air temperature signal as a function of the engine temperaturesignal and the ambient air temperature signal.
 2. The method accordingto claim 1, further comprising the steps of:determining a vehicularspeed signal; determining an induction air signal; and determining acorrection factor as a function of at least one of the vehicular speedsignal and the induction air signal; wherein the induction airtemperature signal is generated as a further function of the correctionfactor.
 3. The method according to claim 2, wherein the induction airsignal represents an induction air mass.
 4. The method according toclaim 2, wherein the induction air signal represents an induction airquantity.
 5. The method according to claim 2, wherein the generatingstep includes the steps of:obtaining a difference value of the enginetemperature signal and the ambient air temperature signal; obtaining amultiplication product by multiplying the correction factor by thedifference value; and subtracting the multiplication product from theengine temperature signal.
 6. The method according to claim 1, furthercomprising the step of filtering the induction air temperature signal.7. The method according to claim 6, wherein the induction airtemperature signal is filtered using a time constant dependent onwhether the induction air temperature signal is rising or falling.
 8. Adevice for generating an induction air temperature signal,comprising:means for providing a temperature signal indicative of atemperature of an internal combustion engine; means for providing anambient air temperature signal; and means for generating the inductionair temperature signal as a function of the engine temperature signaland the ambient air temperature signal.